The present invention relates to the field of turboshaft engines, and in particular to a support for at least one bearing for a hot section of a turboshaft engine, the support comprising a central hub incorporating an outer bearing seat for receiving the bearing, an annular casing segment around the central hub, and a plurality of radial arms connecting said central hub to said annular casing segment.
In the present context, the term “turbine engine” is used to mean any machine for converting the thermal energy of a working fluid into mechanical energy by expansion of said working fluid in a turbine. In the description below, the terms “upstream” and “downstream” are defined relative to the normal flow direction of the working fluid in the turbine engine.
Typically, in such a turbine engine, the working fluid is contained in an annular flow passage between a casing and at least one rotary shaft around a central axis. Said rotary shaft is constrained to rotate together with at least one turbine engine wheel through which said annular fluid flow passage passes. In order to support the wheel, the rotary shaft is supported by at least one bearing, which in turn is supported by a bearing support having a plurality of arms passing radially through the fluid flow passage in order to connect the bearing to the casing of the turbine engine.
Among the various types of turbine engine, there are in particular turboshaft engines. In a turboshaft engine, at least one turbine wheel situated downstream from a compressor and a combustion chamber is coupled to an outlet shaft for taking off the mechanical energy produced by the engine. This distinguishes turboshaft engines in particular from turbojets in which mechanical energy is recovered mainly by the combustion gas expanding in a reaction nozzle. Consequently, in the hot section of a turboshaft engine, i.e. in the combustion chamber and downstream therefrom, thermal stresses are severe because of temperature gradients that are large compared with the size of such an engine. In particular, bearings and bearing supports situated in the hot section are subjected to particularly severe thermomechanical stresses.
In order to accommodate the dynamic stresses on shaft lines and in order to master any tendency of turbines to move off-center while in operation, it is desirable to obtain a high degree of radial stiffness for bearing supports, even at high temperatures. Nevertheless, such great stiffness for a bearing support can have negative repercussions on its lifetime.
In British patent GB 1 010 401, there is described a bearing support for a hot section of a turbine engine in which a central hub is suspended from an annular casing segment of the turbine engine by rods that slope in a radial direction and in a tangential direction. Nevertheless, in order to accommodate thermomechanical forces between the hub and the annular casing section, the ends of those rods are hinged. In addition, the rods are protected by tubular fairings having outer ends that may move longitudinally a little relative to the annular casing section in order to accommodate those same thermomechanical forces. Consequently, that bearing support is very complex, thereby giving rise to high production and maintenance costs.